On Thu, Mar 04, 2021 at 11:28:16PM +0000, Andrew Cooper wrote: > On 04/03/2021 23:09, Boris Ostrovsky wrote: > > On 3/4/21 9:47 AM, Roger Pau Monne wrote: > >> Introduce an option to allow selecting a less strict behaviour for > >> rdmsr accesses targeting a MSR not explicitly handled by Xen. Since > >> commit 84e848fd7a162f669 accesses to MSRs not explicitly handled by > >> Xen result in the injection of a #GP to the guest. This is a behavior > >> change since previously a #GP was only injected if accessing the MSR > >> on the real hardware will also trigger a #GP. > >> > >> This commit attempts to offer a fallback option similar to the > >> previous behavior. Note however that the value of the underlying MSR > >> is never leaked to the guest, as the newly introduced option only > >> changes whether a #GP is injected or not. > >> > >> Long term the plan is to properly handle all the MSRs, so the option > >> introduced here should be considered a temporary resort for OSes that > >> don't work properly with the new MSR policy. Any OS that requires this > >> option to be enabled should be reported to > >> xen-devel@lists.xenproject.org. > >> > >> Signed-off-by: Roger Pau Monné <roger....@citrix.com> > >> --- > >> Changes since v1: > >> - Only apply the option to HVM guests. > >> - Only apply the special handling to MSR reads. > >> - Sanitize the newly introduced flags field. > >> - Print a warning message when the option is used. > >> --- > >> Cc: Boris Ostrovsky <boris.ostrov...@oracle.com> > >> --- > >> Boris, could you please test with Solaris to see if this fixes the > >> issue? > > > > Yes, still works. (It worked especially well after I noticed new option > > name ;-)) > > I'm afraid I want to break and rework how this bugfix happens. Solaris > is still broken on all older branches and this isn't a suitable fix to > backport.
Right, I think that's the reactive part of the fixing that we spoke with Jan, but I think we would still need something similar to rdmsr_relaxed. There's at least one other MSR which Jan identified that we also want to handle MSR_K7_HWCR. Thanks, Roger.
